I'm not saying this just to be condescending, but you do realize that even the Harry Potter books are justified in print, right? (Unless maybe you live in another country and their publishers don't justify their books? Seriously, I don't know.)

I'm glad for the automatic justification of books because it's one less thing for me to worry about editing, re-converting, and verifying in Calibre. I like justification because I like my e-ink pages to resemble print pages as much as possible.

Sorry, I realize that isn't helpful. Just not sure why you dislike it so much. As far as I can tell, all books default to justified. I have a Paperwhite, so I can test your "fix" the formatting option. How were you planning on doing it? Check left align in Look & Feel? I'll try it and report back to you. If there's another way you were thinking of, let me know!

ETA: That works. You can manually convert to a mobi checking left align in Look & Feel and you end up with ragged edges. Hope that's good news for you

Yes, I know the print books are justified. That's how I read them originally. It's something that's only a minor annoyance and doesn't seem to bother me as much in DTB format, but for some reason I find it distracting and uncomfortable on an e-reader.

I've been doing the left align thing when converting my ePubs for use on the Kindle, but those books either came DRM-free or the DRM has been removed. I don't think I've come across the watermarking form of DRM that's used on the HP books, and so didn't know how the conversion process would work. I appreciate you confirming that converting to left alignment would make it the way I want it -- thank you!